1. Field of the Invention
This invention relates to electric reactors. More specifically, this invention relates to a controlled reactive power reactor through the use of magnetic distortion fields.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
At present the electric reactors are the most compact means and the most cost-efficient relation to compensate for the capacitive generation on high-tension lines for long-distance transmission, or long-distance cable systems. Electric reactors are generally used in a permanent service to stabilize the power transmission, or connected only under low-load conditions for voltage control. Although the design aspect of an electric reactor is similar to the one of a power transformer, the input currents, linearity, the generation of harmonics and symmetry between phases are very different.
At present, the most commonly used electric reactor is of the shunt type, also known as “reactor shunt” or the “air gap core”, which can be of the enclosed or column type. The latter is formed by a magnetic core provided by two lateral columns and one central column of air gaps where a main winding is concentrically wound.
The upper ends of the columns are interconnected through an upper yoke whereas the lower ends are interconnected through a lower yoke. The magnetic core is generally formed by stacked sheets that are parallel with the plane where the two lateral columns are located.
The core of the electric reactor of the column type is exactly the central column of air gaps that is generally cylindrical and consists of various ferro-magnetic doughnuts and air-gap spacers embedded between the ferro-magnetic doughnuts. The doughnuts are stacked together in the form of a column. The central column of air gaps must have an elevated elasticity module that reduces the reactor resonance to a minimum, because during the operation of the former, the magnetic field creates intermittent forces through all the air-gap spacers to a point where the forces add up to tens of tons. At present, the elevated elasticity module of the central column of air gaps is obtained while maintaining the union between the ferro-magnetic doughnuts extremely rigid. The air-gap spacers, with the use of epoxy glue and a central pin that passes through the column and maintains the upper and lower yoke together by the use of a bolt-nut mechanism, allows the elimination of the vibrations during the operation of the reactor.
The structure of the electric reactor described above presents the inconvenience that over time, in spite of the mechanism used to maintain the central column of air gaps rigid, generates considerable noise due to the vibration of the air-gap spacers located between the different ferro-magnetic doughnuts that are compressed. The precision, that was adjusted when mounting the frame of the central column at the start connecting it to the yokes of the core, diminishes. The unfavorable phenomenon is presented particularly, if due to inexactness of the thickness and height dimensions of the air-gap spacers and the ferro-magnetic doughnuts, or if because of an elasticity difference or decrease differences of the different air-gap spacers, the upper yoke does not rest equally on all the columns of the core frame. A solution to this disadvantage is described in the Spanish patent ES-340,896.
Added to the former, depending on the required application of the electric reactor, the latter can involve an adjustment or regulation of the relation of reactive power in one or more steps. At present, it is common to do this by means of load tap changers, or through a semi-permanent adjustment of the relation of turns of the main winding by one or more steps when the reactor is disconnected via the load taps. The adjustment or regulation of the relation of reactive power of the reactors in the distribution network is necessary to be able to guarantee a stabilization of the power transmission and the capacitive generation on long-transmission high-tension lines or in long-distance cable systems.
Another current solution to reach an adjustment of the reactive power with precision and speed is the technology known as a “Magnetically Controlled Reactor” (MCR) developed by Alexander M. Bryantsev et al. Its functioning principle is first based on directly controlling the magnetic flow in the reactor core, while some of the winding turns are periodically taken into short-circuit by means of the semiconductor interrupters and/or provoking magnetically the core saturation. The former are described in the Russian patents RU-989,597, RU-2,231,153, RU-2,132,581 and RU-2,141,695.
At present, electronic switches are also used in the form of transistors or thiristors. Such a solution is described by Paulus G. J. M. Asselman et al. in the publication of the Mexican patent application MX-9800816, which refers to a method and a device to continually adjust, within a determined adjustment interval, the transformation relation or the amount of turns between the primary winding and the secondary winding of a power transformer provided by at least one regulator winding, where a first outlet is connected during part of a cycle of the alternate voltage of the transformer and a second outlet is connected during other part of the cycle of the alternate voltage.
Also common is the use of interlaced or crossed windings, as described by Andre Kislovski in the Spanish patent ES-2,001,118, where an electrically adjustable construction inductive element is shown, that consists of two ferro-magnetic cores magnetically independent from each other, equal, annularly enclosed that individually carry the partial windings of an induction winding and together they carry the controlling operation coil. The direction of the turning of the partial windings and the induction is such that the generated magnetic fields in one of the cores are mutually weakened by currents through the windings, while being increased in the other core.
Another alternative current solution to provide a variable reactor is to use two or more magnetic cores, linked with common core elements as described by Gregory Leibovich in the U.S. Pat. No. 4,837,497, illustrating a transformer or variable reactor with as a base the combination of at least two cores with a common yoke. The primary winding is divided in two independently fed sets of phase coils wound in opposed directions, arranged on symmetrical legs and columns of the cores and separated by the common yoke. The secondary winding with each phase coil divides into two parts and is wound in opposite directions on the symmetric core legs of the base, adjacent to the parts of the primary coil and separated by the common yoke. The winding of secondary short circuits of the transformer or reactor is reduced to at least one close loop member with loop portions separated by the common yoke. The polyphasic apparatus has at least one primary coil per set that includes a controllable device in circuit relation therewith to enable control of one primary coil relative to the other, either in current magnitude or in current phase shift. The controllable device is a rectifier, TRIAC or transistor. Therefore, having continuous control of the controllable device, an apparatus with variable output parameters is obtained.
Another alternative to provide a reactor of controllable reactive power consists in forming a reactor with a magnetic core whose structure has movable elements, or with displacement that allows forming a variable air space in the core. This brings about a change in the magnetic flow induced by the windings, thus allowing a control of the reactive power in a linear or gradual way. The control of the movement in movable elements for opening and closing of the variable air space of the core, may be performed by mechanisms of manual, semi-automatic or automatic displacement control. An example of this application is described by Steven Hahan in U.S. Pat. No. 4,540,931, which shows a transformer that includes a system for control of electric output voltage that uses a core with movable structure. The electric output voltage of the transformer is perceived and the latter makes itself corresponded to a predetermined standard movement of the movable structure, which is then blocked when positioned in the correct location. The changes in electric voltage are free of steps and the linear control of the electric voltage in relation to the time is reached through the non-linear movement of the movable structure, allowing a wide range of variation in the electric output voltage.
Another present variation to provide an electric reactor of controlled reactive power is described by Kurisawa Hideakin in the Japanese patent JP-11144963, where the electric reactor consists of a conductive cylinder which is externally concentric to the winding and in electric contact with the latter so that the cylinder makes itself displaced in a controlled manner along the winding axis with the help of a displacement mechanism with the aim of obtaining a certain amount of turns of the winding to enter into short circuit, thus allowing to vary the reactive power of the reactor.
The aforementioned solutions represent complex control systems that require load taps switches controlled by mechanical devices, a reconfiguration of the winding turns or of the magnetic core, and/or use of mechanical or servo-mechanic equipment applicable to the formation of variable air space in the magnetic core, as well as the use of mechanisms that maintain the rigid structure of the core, all the former to provide a reactor of controlled reactive power. Therefore, it is necessary to provide an electric reactor of controlled reactive power which allows adjusting the reactive power under load or not, in a simple and economic way in the distribution networks with major precision, speed and a wide operational range, as well as to maintain the rigid structure during its operation time compared with the state of the art, through the use of magnetic distortion fields in the reactor core.